Anion redox as a means to derive layered manganese oxychalcogenides with exotic intergrowth structures

Topochemistry enables step-by-step conversions of solid-state materials often leading to metastable structures that retain initial structural motifs. Recent advances in this field revealed many examples where relatively bulky anionic constituents were actively involved in redox reactions during (de)intercalation processes. Such reactions are often accompanied by anion-anion bond formation, which heralds possibilities to design novel structure types disparate from known precursors, in a controlled manner. Here we present the multistep conversion of layered oxychalcogenides Sr2MnO2Cu1.5Ch2 (Ch = S, Se) into Cu-deintercalated phases where antifluorite type [Cu1.5Ch2]2.5- slabs collapsed into two-dimensional arrays of chalcogen dimers. The collapse of the chalcogenide layers on deintercalation led to various stacking types of Sr2MnO2Ch2 slabs, which formed polychalcogenide structures unattainable by conventional high-temperature syntheses. Anion-redox topochemistry is demonstrated to be of interest not only for electrochemical applications but also as a means to design complex layered architectures.

1. In the middle of the multi-step reaction (STEP2,4 in Fig.1), disulfiram was used to remove the precipitated Cu. Is there another way to remove Cu? Also, in view of the synthesis of new materials using anion redox, for example, is it not possible to perform the reaction of STEP 5 after STEP 1? Besides, is it possible to directly react Sr2MnO2Cu1.5Ch2 with disulfiram without going through an intermediate phase?
2. It is stated that the obtained "collapsed" phase returns to the original precursor with the I4/mm structure after electrochemical lithium intercalation or reaction with n- BuLi (p.13,. Do the stacking faults found in the "collapsed" phase (as seen in e.g., Fig.4) disappear and return to the original structure after these reactions? 3. Is the obtained "collapsed" phase stable in the atmosphere? Is there any possibility that the composition or structure will change over time?
4. What is the reason why the novel layered compound Sr2MnO2S2 containing (S2)2-dimers and its intergrowth structure could not be synthesized in their single phases? For example, is it because the structural stability of Sr2MnO2S2, intergrowth structure compounds, and precursor Sr2MnO2Li1.9S2 are energetically competing? It may be considered that by calculating the total energy and phonon dispersion of these compounds, it would be possible to evaluate the thermodynamic stability of these compounds and clarify this reason.
Minor point I thought it might be good to move the sentence about the details of the Rietveld analysis described in the second paragraph on page 13 to Supporting Information. The stacking faults and random distribution of intergrowth structures of the "collapsed" phase discussed in this paragraph seemed to be already clarified from experiments of STEM and EDX elemental mapping. Therefore, the reason for repeating the Rietveld analysis seemed unclear. I thought that the authors had a great effort for the Rietveld analysis with the periodic structural model and carefully performed the analysis. However, in the end, the authors concluded that the structural model considered here could not reasonably reproduce the diffraction peak intensity. Therefore, it seemed to me that the claim from the Rietveld analysis here is ambiguous.
(END of comments) Reviewer #2 (Remarks to the Author): This is a high-quality work about topochemical reaction of layered oxychalcogenides. The author reported multi-step Cu-deintercalation of Sr2MnO2Cu1.5Ch2 yielding the collapsed phase with Ch2 dimers. The (almost) full deintercalation of Cu from Sr2MnO2Cu1.5Ch2 phase is the first case, but a similar concept was already reported by the authors in the other layered oxychalcogenides (e.g. ref 14; La2O2Cu2S2). The impressive point in this work is the controlled chemical reactions: They used an organic reagent, disulfiram, which seems to work as a chemoselective agent toward Cu. Their characterization of the collapsed phase is well done in that they used several methods to determine the structural and chemical states. Especially, they carried out advanced Rietveld analysis to fit the XRD pattern with defects or stacking faults. I consider that this work is important for the fundamental interests of solid-state chemistry fields, and is worth publishing in Nat. Commun.
Additional comment: I feel that the five-step-reaction is one of the most important part of this work. But there are no figures to see how XRD patterns changes in each reaction (There are some XRD patterns in supporting information but they are not whole reactions). I recommend that the authors put the five XRD patterns in the main figure.
Reviewer #3 (Remarks to the Author): Sasaki and coworkers report on the topochemical manipulation of a layered mixed-metal oxychalcogenide compounds. Sequential reaction steps involving copper extraction and lithium intercalation/deintercalation result in a series of topochemically related intermediates, culminating in a "collapsed" structure with new sulfur/selenium dimers. This result is exciting in that it shows the rigorous extraction of intermediate layers can be carried out while still retaining key structural features (MnO layers) of the parent compound. The researchers are thorough in their treatment of this system, including detailed X-ray, neutron, and electron diffraction studies. The electron diffraction studies are especially illuminating as to the concurrent complexity and beauty of the final products.

NCOMMS-22-52782-T Anion Redox as a Means to Derive Layered Manganese Oxychalcogenides with Exotic Intergrowth Structures S. Sasaki et al.
Response to Reviews.

Reviewer #1 (Remarks to the Author):
Review report for NCOMMS-22-52782-T Anionic redox-based topochemical reactions have attracted attention in recent years due to their ability to improve the performance of battery materials and synthesize new inorganic compounds containing anionic molecules. In this study, the authors focused on Sr2MnO2Cu1.5Ch2 (Ch = S, Se) with the alternative stacks of Sr2MnO2 and Cu1.5Ch2 layers, and in particular, Cu deintercalation in Cu1.5Ch2 layers from topochemical reactions utilizing the anionic redox of the formation/deformation of (Ch2) 2dimers in conjunction with the synthesize of a new compound. Attempts have been made to remove Cu in Sr2MnO2Cu1.5Ch2 but conventional reaction methods using e.g., I2 and Br2 have not been able to extract Cu sufficiently. Therefore, research from a new viewpoint was necessary. In this study, the authors proposed the use of the intermediate phase of the Li + /Cu + exchanged compound to lower the activation barrier, and also selectively removed the precipitated Cu with disulfiram. By using this Li-exchanged intermediate phase as a precursor for the topochemical reaction, they demonstrated the synthesis of a novel layered compound containing (Ch2) 2dimers.
This research is interesting in view of the development of a new reaction route and synthesis of a compound previously inaccessible, through an intermediate phase. However, this manuscript focused on somewhat technical matters, including the reaction and the structural analysis of the obtained material, and it seemed unclear what was important as scientific knowledge. For example, it may be found that it is better to use disulfiram while probably considering the HASB theory, etc., but it seemed unclear in this manuscript from what point of view the chemically selective reagent was chosen. The generality and scalability of the chemical reactions dealt with in this study also seemed unclear.
The material obtained in this study may be a novel layered compound containing (S2) 2-(or (Se2) 2-) dimers. However, at present, stacking faults and intergrowth structures exist randomly, i.e., it could be an impure mixture. In addition, even if Li can be electrochemically inserted, there is a limit to sufficiently removing Li again, resulting in a limit to the development of applications such as batteries.
In this research, it is important to focus on anionic redox and develop multi-step topochemical reactions. It was thus thought that the manuscript would be better if there was a clear description of how the strategy for the synthesis of new compounds and an understanding science behind this.

Response:
We thank the referee for these constructive suggestions. We understood the overall concern from the referee that the manuscript focused on technical matters, and therefore further discussion was added to elaborate on the scientific ideas behind our synthetic route, perspectives for further applications & challenges to be tackled. The following are a point-bypoint responses to the referee's major concerns.
• "…it may be found that it is better to use disulfiram while probably considering the HASB theory, etc., but it seemed unclear in this manuscript from what point of view the chemically selective reagent was chosen"  As the referee suggested, our motivation for lithiation is based on HSAB theory. Small, hard-acidic Li + cations are less compatible with tetrahedral sites surrounded by soft-basic S 2anions than more soft-acidic Cu + cations. Accordingly, we hypothesized that Li + could be removed more easily from the host oxychalcogenides.
To clarify this, we added the phrase in Page 6: "Compared to the soft-acidic Cu + intercalants, the smaller, hard-acidic Li + cations can be removed more easily from the soft-basic sulfide layers." As for the choice of disulfiram, its primary reason is the excellent chemoselectivity toward Cu 0 dissolution as already mentioned in the manuscript.  (2015)). The below figure is the XRD pattern of the by-products that we collected from the supernatant solution of the Step 2 reaction. Our cursory Rietveld fit used only the model of Cu(II)bis(N,N-diethyldithiocarbamate) but qualitatively explained most of its diffraction peaks. This reflects the strong preference of disulfiram to form complexes with Cu over Li. As we already presented in Fig. S3, less chemoselective reagents such as I2 gave the completely opposite results through Li + deintercalation and Cu re-intercalation into the host lattice. Another reason to choose disulfiram is its molecular structure. Disulfiram has a stable, covalently bonded molecular skeleton made of C, N, S and non-acidic protons. As noted already in the introduction, oxidizing agents based on halogens and nitronium ions (e.g. I2 at above 0 °C, Br2, NO2BF4) tend to decompose Sr2MnO2Cu1 (2016)), which ended up with decomposition of the host oxysulfide into SrCl2 etc. Besides halogens, we also wanted to avoid reagents containing acidic protons that often destroy Li-S compounds. That was the reason why we did not use other well-known metal chelating agents such as EDTA and Salicylaldoxime. So far, we regard disulfiram as the best reagent to synthesize the collapsed phase but all of the above criteria may be applied to other reagents. Especially, further optimization of its molecular structure would be a useful avenue for future research rather than simply using commercially available reagents.
Based on the above discussion, we added the following sentences in page 7: "Equally, one must properly design oxidizing agents so that they selectively dissolve elemental Cu without affecting the rest of the host framework. For example, the reaction of the Step 1 product with I2 in acetonitrile, a conventional oxidant for chemical deintercalation, simply restored the parent phase through Li deintercalation and almost complete Cu reinsertion without any Cu dissolution (Fig. S3) • "The generality and scalability of the chemical reactions dealt with in this study also seemed unclear."  In our study, we have successfully applied the chemical route not only to the sulfide but also the selenide. As for future perspective, we currently confirmed that the similar chemical route could be applied to the whole Sr2MnO2Cu2m-δSm+1 (m = 1-3) homologous series. There are also many other known compounds made of anti-fluorite type copper chalcogenide layers. Disulfiram may serve as effective reagents to remove copper, either directly from the host lattice triggering collapses of the layers (although that is not successful in this case -see below), or indirectly via the Cu-Li exchange steps used in this case.
To discuss generality of the reactions, the following sentences were added in page 18: "Accordingly, our current efforts are aimed at extending the scope of this chemical route to the whole Sr2MnO2Cu2m-δSm+1 (m = 1-3) homologous series 30 . Cu extrusion through topochemical Cu-Li exchange is widely known among metal chalcogenides but mostly studied in the context of Li-ion battery applications [51][52]  • "…even if Li can be electrochemically inserted, there is a limit to sufficiently removing Li again, resulting in a limit to the development of applications such as batteries."  We agree with the referee on the limited electrochemical cyclability of the collapsed phase. As shown in Fig. 4d In future the in-depth analyses of electrochemical behaviour may provide us a guide to circumvent the potential barrier, rendering the collapsed phase (or its variants) promising as cathode materials.
We are currently working to improve our understanding of the electrochemical behaviours of this phase. Our preliminary studies suggest that the reduction of this collapsed phase follows a straightforward intercalation mechanism, unlike the Li-Cu exchange seen for Cu analogues. The kinetic barrier for S 2oxidation to form S-S bonds appears to cause the voltage hysteresis. Since this analysis is ongoing we thus added a short discussion concerning the challenges (See page 12): "The subsequent charging step in Fig. 4d 38,40 . The presence of residual Cu may also play a role in this hysteresis, as seen previously in the Cu-system 46 . In any case, such kinetic barriers also hint at why the chemical deintercalation at Step 6 ( Fig. 1a)

could not remove all Cu/Li cations from the final product. Further in-depth analyses of its reaction dynamics are currently ongoing, employing in-or ex-situ spectroscopic and diffraction techniques."
The followings are other points that seemed unclear: 1. In the middle of the multi-step reaction (STEP2,4 in Fig.1), disulfiram was used to remove the precipitated Cu. Is there another way to remove Cu? Also, in view of the synthesis of new materials using anion redox, for example, is it not possible to perform the reaction of STEP 5 after STEP 1? Besides, is it possible to directly react Sr2MnO2Cu1.5Ch2 with disulfiram without going through an intermediate phase? Response: • "Is there another way to remove Cu?"  It may be possible to remove the extruded elemental Cu 0 using the proper oxidizing agents similar to disulfiram: strong preference to chelate Cu 2+ over Li + , non-acidic, nonhalogenic molecules with stable covalently-bonded skeletons. We did not perform extensive screening since disulfiram has already exhibited good performance. On the other hand, it is much more rewarding to attempt to dissolve Cu at the same time with Cu-Li exchange (Step 1) since such one-pot removal of Cu from the system would significantly simplify the synthetic scheme. It is not easy to dissolve Cu under the presence of a strong reducing agent like n-butyllithium, but we made some attempt to dissolve Cu as organolithium cuprates by adding lithium bromides and alkyldiamines. So far these efforts haven't seen any success, but we continue to explore this possibility from various approach.
Following the query from the referee, we added the sentence in page 7: "We also tried to dissolve Cu + cations at Step 1 as organolithium cuprates 26 before they are reduced to elemental Cu 0 but these attempts were so far unsuccessful. Nevertheless, the one-pot removal of Cu would significantly simplify the synthetic procedure and therefore this will be one of our next challenges in synthetic methodology." • "…is it not possible to perform the reaction of STEP 5 after STEP 1?"  The difference between Step 2 and 5 is just their reaction temperature. Therefore, " Step 5 after Step1" process must necessarily go through Step 2 reaction unless hot solution (T = 80 °C) were rapidly injected into Step 1 product, which would make the exothermic reaction with disulfiram too violent to be controlled. In the case of Step 1→2→5, this route also give the XRD pattern similar to that of the proper 5-step product (Fig. 2a). However, skipping Step 3-4 would end up with increased Cu content in the final product. Our present study aimed at removing Cu as much as possible to synthesize the new compounds, and therefore we did not pursue this shortcut pathway that produces more impurity "parent-type" stacks.
• "…is it possible to directly react Sr2MnO2Cu1.5Ch2 with disulfiram without going through an intermediate phase?"  In the same way with a commonly used oxidizing reagents like I2, disulfiram can be used for partial Cu deintercalation from Sr2MnO2Cu1.5Ch2 without going through a synthetic intermediate. The figure below displays PXRD patterns before and after the direct reaction of Sr2MnO2Cu1.5S2 with disulfiram. After the reaction at 80 °C, the diffraction peaks exhibited small but visible shifts toward higher angle. Rietveld refinement using the Sr2MnO2Cu1.5S2 structural model estimated the cell parameters to be a ~ 4.00 Å and c ~ 17.06 Å, comparable to those for the Sr2MnO2Cu1.5-xS2 phase (x < 0.17) that we previously obtained after treatment by I2 at 0°C (For details: Blandy J. et al. APL Mater. 3, 041520 (2015)). Unlike I2, disulfiram did not decompose the host oxysulfide even above 0 °C. We can therefore recommend disulfiram as a non-volatile, non-corrosive, and non-hygroscopic alternative to I2 or other common reagents used for deintercalation. Nevertheless, disulfiram alone was not sufficient to escape from the potential landscape of the "parent-type" I4/mmm structures and to reach the collapsed phase directly in this case.
The below figure was added as Fig. S2 in the supporting information. We also added the following sentences in page 6: "The combination of the lithiation steps and the selective dissolution of the extruded elemental Cu was essential to reach the final "collapsed" phase. We also treated the parent Sr2MnO2Cu1.5S2 phase with disulfiram without the lithiation step (Fig. S2), but the reaction even at elevated temperature (T = 80 °C) reduced its cell parameters only to the extent comparable to our previous attempt to oxidize Sr2MnO2Cu1.5S2 using I2 at 0°C,15 which deintercalated Cu by about 10%. This result suggests a large activation barrier between the parent phase and the "collapsed" phase that must be circumvented by going through reactive intermediates." of the crystal and magnetic structure of a layered mixed valent manganite oxide sulfide APL Mater. 3, 041520 (2015).

Fig. B. X-ray diffraction (XRD) patterns after the reaction of Sr2MnO2Cu1.5S2 with disulfiram.
Zoom-in views of the laboratory powder XRD patterns of pristine Sr2MnO2Cu1.5S2 (black) and the products after its treatments with excess (6.0 equiv.) of disulfiram in DMF solution at ambient temperature (blue) and at 80 °C (red). Rietveld refinements using the respective patterns indicated that the treatment with disulfiram led to small cell contraction of the Sr2MnO2Cu1.5S2 structure model, but to the extent not greater than Sr2MnO2Cu1.5-xS2 phase (x < 0.17) reported by Blandy J. et al. APL Mater. 3, 041520 (2015).
2. It is stated that the obtained "collapsed" phase returns to the original precursor with the I4/mmm structure after electrochemical lithium intercalation or reaction with n-BuLi (p.13, lines 11-16). Do the stacking faults found in the "collapsed" phase (as seen in e.g., Fig.4) disappear and return to the original structure after these reactions?
Response: After Li intercalation using n-BuLi, its XRD pattern (Fig. S22) no longer exhibited severe hkldependent and/or anisotropic peak broadening unlike the collapsed phase. This suggested good crystallinity of the recovered Sr2MnO2LixS2 phase with the parent-type I4/mmm structure. More importantly, its 7 Li NMR spectra after chemical or electrochemical lithiation no longer displayed the peaks arising from the intergrowth-type stacks (Fig. 6b-c). The 7 Li NMR peak centered around 400 ppm are characteristics of Li in parent type structure, as seen earlier by our groups in a separate study (ref [34]: Indris, S. et al. J. Am. Chem. Soc. 128, 13354-13355 (2006)), thus indicating that these lithiated phases were more or less free (at least on NMR) from stacking faults made of the "collapsed" type slabs.
To emphasize the point, we added the following sentences in page 16: "The multiple high frequency peaks above around 600 ppm have disappeared after chemical or electrochemical lithiation (Fig. 6b-c). Their NMR shift could fully be explained by the parent type structure with different Mn 2+/3+ ratios showing hyperfine interaction via Mn 2+/3+ -S-Li interactions. This suggested that most of the "collapsed" type stacks were removed upon lithiation and its product no longer suffered from the severe stacking disorders." 3. Is the obtained "collapsed" phase stable in the atmosphere? Is there any possibility that the composition or structure will change over time?
Response: Both "collapsed" oxysulfide and oxyselenide were stable under air (12-24h of air exposure) or over time (left under Argon over 3-6 month) without any sign of degradation on its diffraction pattern, morphology and reactivity toward lithiation. Air stability of the "collapsed" oxysulfide is highlighted in its formation from Sr2MnO2LixS2 upon air exposure (See the below figure). Once most of Cu had been removed from the system, a part of the Sr2MnO2LixS2 phase spontaneously turned into the collapsed phase with the diffraction peak at d ~ 7.9 Å via aerial deintercalation of Li. The example shown below was for the Step 3 product Sr2MnO2LixS2 + y Cu (x ~ 1.9, y ~ 0.1), but the same was observed for the pure Sr2MnO2LixS2 phases (Fig. S22) that were obtained by re-lithiation of the collapsed oxysulfide using n-BuLi. None of these Sr2MnO2LixS2 samples, regardless of Li content x, could remain single phase after air exposure and they were partially converted into the collapsed phase once Cu had been removed from the system and could not reintercalate to compensate aerial Li deintercalation.

Fig. C. X-ray diffraction (XRD) patterns of the lithiated
Step 3 products before and after air exposure. Air exposure of the Step 3 product Sr2MnO2LixS2 + y Cu (x ~ 1.9, y ~ 0.1) led to emergence of the new peak at around 7.9 Å, indicating the formation of the collapsed phase as a minor phase.
The above figure (Fig. C) was added in the supporting information as Fig. S4. We also added the corresponding discussion in page 7 of the manuscript: "In contrast to such inaccessibility of the collapsed phase from Sr2MnO2Cu1.5S2, this oxidized phase was stable under air and spontaneously formed from Sr2MnO2LixS2 by aerial deintercalation of Li once most of Cu had been removed from the system by the disulfiram. For example, air exposure of the Step 3 product (i.e. Sr2MnO2LixS2 + 0.1 Cu) led to emergence of a small XRD peak at 7.9 Å (Fig. S4), indicating the formation of the collapsed phase as a minor phase. Similar XRD patterns were observed also in Step 2 and 4 products (Fig. 1c). These results suggest the presence of the collapsed phase as the product of aerial surface oxidation." 4. What is the reason why the novel layered compound Sr2MnO2S2 containing (S2) 2dimers and its intergrowth structure could not be synthesized in their single phases? For example, is it because the structural stability of Sr2MnO2S2, intergrowth structure compounds, and precursor Sr2MnO2Li1.9S2 are energetically competing? It may be considered that by calculating the total energy and phonon dispersion of these compounds, it would be possible to evaluate the thermodynamic stability of these compounds and clarify this reason.
Response: This is a difficult question to answer before carrying out comprehensive mechanistic studies of its intercalation chemistry using both theoretical and experimental approaches. At the moment, we suspect that the removal of Cu/Li intercalants was limited rather for kinetic reasons than thermodynamic stabilities for the following reasons: (1) large voltage hysteresis during electrochemical Li deintercalation from Sr2MnO2Li2S2 (Fig. 4d) and (2) spontaneous formation of the collapsed phase from the parent-type Sr2MnO2LixS2 phases upon air exposure (Fig. C). As discussed in our responses above, such voltage hysteresis was commonly observed during oxidation of anionic species (See e.g. Li, B., Sougrati et al. Nat. Chem. 13, 1070-1080) and this kinetic barrier was sometimes associated with sluggish structural distortions. Considering its large structural transformation, it is possible that the formation of the collapsed phase involves significant kinetic barriers. It might be possible that the collapsed phase is not thermodynamically favourable compared to its chemical variants Sr2MnO2LixS2 (parent type) or intergrowth phases, but in this case the parent-type Sr2MnO2LixS2 would not turn into the collapse phase unless highly oxidizing conditions were applied. However, what we observed was the spontaneous oxidation of the parent-type Sr2MnO2LixS2 into the collapsed phase, even under very mild oxidizing conditions like air exposure (See Fig. C in our response above). Complete conversion into the collapsed phase was blocked, possibly due to kinetic reasons, and required the reaction with disulfiram at elevated temperature (80 °C).
To fully understand what obstructed complete Cu/Li removals, we must therefore investigate how oxidation takes place and how the structures evolve during the formation of collapsed phase, employing various in-situ/ex-situ characterizations. We believe that such a comprehensive study should be published in separate full paper. It is also a good idea to compute total energy and phonon dispersion of the relevant compounds. However, this would equally require systematic and comprehensive investigation considering e.g. various Li content x in the parent-type Sr2MnO2LixS2 (1 < x < 2) and intergrowth-type [Sr2MnO2S2][Sr2MnO2LixS2]. Li contents in these phases are directly linked to Mn 2+/3+ or S 2-/oxidation states, and eventually affecting local structure and stability of the Sr2MnO2S square lattice (See for example: H.-J. Koo et al. Inorg. Chem. 2019, 58, 21, 14769-14776). Given their extent and demanding nature, we prefer that these calculations will be done as a separate and mechanism-oriented full paper.
These comprehensive mechanistic study is ongoing in our group. To signal our intention, we added the following sentences in page 12: "…In any case, such kinetic barriers also hint at why the chemical deintercalation at Step 6 ( Fig. 1a) could not remove all Cu/Li cations from the final product. Further in-depth analyses of its reaction dynamics are currently ongoing, employing in-or ex-situ spectroscopic and diffraction techniques." A similar mention was added also to page 18-19: "We are currently investigating how the competition between Mn 2+/3+ and S 2-/-redox evolves during Li (de)

intercalation processes as well as the complex reaction dynamics both from thermodynamic and kinetic points of view."
Minor point I thought it might be good to move the sentence about the details of the Rietveld analysis described in the second paragraph on page 13 to Supporting Information. The stacking faults and random distribution of intergrowth structures of the "collapsed" phase discussed in this paragraph seemed to be already clarified from experiments of STEM and EDX elemental mapping. Therefore, the reason for repeating the Rietveld analysis seemed unclear. I thought that the authors had a great effort for the Rietveld analysis with the periodic structural model and carefully performed the analysis. However, in the end, the authors concluded that the structural model considered here could not reasonably reproduce the diffraction peak intensity. Therefore, it seemed to me that the claim from the Rietveld analysis here is ambiguous.
(END of comments) Response: We agree with the referee on the point that our attempts to take Cu/Li into account could not provide further information beyond STEM and EDX due to unconvincing Rietveld fit to the XRD pattern. Accordingly, we made the discussion shorter and more concise (See below). Nevertheless, we believe that the attempt must be mentioned in the main text so that readers will be able to understand why we could not provide a refined structure model with Cu and Li cations reproducing the experimental diffraction patterns. We thus did not removed the entire discussion from the main text.
We simplified the former half of the corresponding discussion in page 14 as follows: "The presence of both parent phase and intergrowth layers alongside the collapsed layers encouraged us to attempt Rietveld refinements explicitly taking the presence of these residual Cu and Li cations into account. A custom-built code generated ~20000 unique 1500-layer supercell models containing different combinations of those three structures (See section 3.4 in the SI for details)." Also, we added the sentences to relate the discussion to following NMR results: "Bulk probes like XRD have an apparent limit to analyze stacking faults in such spatially heterogeneous samples, and they must be complemented by local probes." Similar point was emphasized in the conclusion (page 19): "We modelled the presence of these residual Cu + and Li + cations using stacking faults in which monoclinic Sr2MnO2Ch2 regions intergrow with parent-type Sr2MnO2Cu1.5S2 slabs, but our Rietveld analysis could not explain their compositional and structural heterogeneity. On the other hand, our local probe analyses using HAADF-STEM imaging and 7 Li NMR revealed that substantial regions consisted of periodic intergrowths of Sr2MnO2Ch2 and Sr2MnO2(Cu,Li)2S2type layers." This is a high-quality work about topochemical reaction of layered oxychalcogenides. The author reported multi-step Cu-deintercalation of Sr2MnO2Cu1.5Ch2 yielding the collapsed phase with Ch2 dimers. The (almost) full deintercalation of Cu from Sr2MnO2Cu1.5Ch2 phase is the first case, but a similar concept was already reported by the authors in the other layered oxychalcogenides (e.g. ref 14; La2O2Cu2S2). The impressive point in this work is the controlled chemical reactions: They used an organic reagent, disulfiram, which seems to work as a chemoselective agent toward Cu. Their characterization of the collapsed phase is well done in that they used several methods to determine the structural and chemical states. Especially, they carried out advanced Rietveld analysis to fit the XRD pattern with defects or stacking faults. I consider that this work is important for the fundamental interests of solid-state chemistry fields, and is worth publishing in Nat. Commun.
Additional comment: I feel that the five-step-reaction is one of the most important part of this work. But there are no figures to see how XRD patterns changes in each reaction (There are some XRD patterns in supporting information but they are not whole reactions). I recommend that the authors put the five XRD patterns in the main figure. Response: We appreciate the encouraging feedback and the useful suggestion from the referee. Following the referee's advice, we combined the XRD patterns at each synthetic step (Originally Fig. S1 and S3) with Fig. 1a. Accordingly, the original Fig 1b-d were separated as the independent Fig. 2.